BANGKOK — A prominent Thai activist and magazine editor was sentenced to a decade in prison Wednesday for defaming Thailand’s monarchy, a verdict rights groups condemned as the latest affront to freedom of expression in the Southeast Asian country.

Somyot Pruksakasemsuk was convicted of publishing two articles in an anti-establishment magazine that made negative references to the crown.

The verdict came despite repeated calls by rights groups to free Somyot, who has been jailed since 2011. It also underscored the harsh nature of Thailand’s lese majeste laws, which critics say have frequently been used by politicians to silence rivals.

The articles were published under a pseudonym in Somyot’s now-defunct Voice of Taksin magazine, which he launched in 2009 to compile political news and anti-establishment articles from writers and contributors.

Judges found both articles included content that defamed the royal family and argued that Somyot, as a veteran editor, was aware of that. The court handed down two five-year jail terms — one for each story.

Somyot “should have better judgment than ordinary journalists. He must have understood that the articles contained lese majeste content, but chose to publish them anyway,” one of judges said in the ruling.

Somyot said he would appeal the verdict but would not seek a royal pardon.

Navi Pillay, the U.N. high commissioner for human rights, said the harsh sentence “sends the wrong signals on freedom of expression in Thailand.”

“The court’s decision is the latest indication of a disturbing trend in which lese majesty charges are used for political purposes,” she said in a statement.

Pillay said she was also concerned about the length of Somyot’s pre-trial detention, the denial of his 12 bail requests, and his appearance in court in shackles.

“People exercising freedom of expression should not be punished in the first place,” she said.

The European Union said the verdict “seriously undermines the right to freedom of expression and press freedom” and “affects Thailand’s image as a free and democratic society.”

Brad Adams, Asia director of Human Rights Watch, said the ruling “appears to be more about Somyot’s strong support for amending the lese majeste law than about any harm incurred by the monarchy.”

Although the articles were published in 2010, Somyot was not arrested until the following year — five days after launching a petition drive to revoke Article 112 of the nation’s criminal code, which mandates three to 15 years in jail for “whoever defames, insults or threatens the king, the queen, the heir to the throne or the regent.”

Human Rights Watch said the author of the articles has never been charged with any crimes and is living in Cambodia.

More than 100 observers, including Thai and international scholars and diplomats, were in court to hear the verdict.

Somyot was also sentenced to an additional one-year term in a separate criminal case for alleging that a Thai general helped fund the country’s 2006 army coup.

The coup ousted Prime Minister Thaksin Shinawatra and sparked years of sometimes violent political unrest from which the nation has yet to fully recover. Somyot was a leader of the “Red Shirt” movement which supported Thaksin.

“His guilty verdict and sentence should be viewed as a sign that Thailand’s deep political schisms are far from healed,” said Adams of Human Rights Watch.